Water Balance of savannah woodlands: A modelling study of the Sudanese gum belt region

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In arid and semi-arid environments, water availability is the main factor limiting plant growth, productivity and distribution, and is strongly related to the amount of rainfall and evapotranspiration. Water quantity is a prime attribute of the water services provided by ecosystems and is best described by using a water balance. While much is known about the water balance of forest ecosystems in boreal and temperate climates, less is known about those in the tropics. The overall aim of this study was to determine and evaluate the water balance of savannah woodlands across the Sudanese Acacia gum belt region.

The study was carried out across the 39 map sheets (1:250,000; 1.0° lat. x 1.5° long.) covering the gum belt region (10-16° N). A water balance model, WATBAL, was parameterized for Acacia dominated woodland vegetation and two dominating soil types, arenosols (AR) and vertisols (VR) (to 1 m depth) and used to estimate mean annual actual evapotranspiration (AET), surface runoff and drainage. For each of the map sheet, necessary long-term mean climate data (precipitation, temperature and sunshine hours) were derived from the FAO local climate estimator, LocClim and soil data from HWSD database.

Mean annual precipitation (MAP) varied across the study region from 146 to 733 mm and mean annual temperature from 24.2 to 29.2 °C. AET was strongly limited by MAP. Mean annual AET was slightly higher for VR soils (ranging from 146 to 670 mm) than for AR soils (ranging from 146 to 653 mm) reflecting the greater plant available water capacity of VR soils. Surface runoff was also higher for VR soils (ranging from 0 to 89 mm) than for AR soils (ranging from 0 to 109 mm). There was no drainage for VR soils but AR soils produced drainage for few map sheets (maximum 68 mm). The region has suffered from considered degradation, and stocking densities are below capacity. The restoration of woodlands may be expected to improve soil water conditions.
Original languageEnglish
Title of host publicationForests and Trees: Serving the People of Africa and the World : IUFRO-FORNESSA Regional Congress & ITTO/AFF Forest Policy Day
Number of pages202
PublisherKenya Forestry Research Institute
Publication date2012
Publication statusPublished - 2012
MoE publication typeA3 Book chapter

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